True, he hasn’t said the magic words “I’m in.” He doesn’t have an official campaign staff. There aren’t authorized “Biden 2016” hats.

But the sitting VP is actively participating in the larger search for Democratic Party support that experts call “the invisible primary.” That’s what his highly visible recent meetings with fundraisers, labor leaders, and other party figures are all about.

After all, it’s the invisible primary’s informal ideological network that vets candidates, steers donors, and sends signals to grass-roots activists and ordinary voters about whom to support. They’re the gatekeepers. If they give Mr. Biden enough encouragement, he’ll take the next step and officially announce.

If they don’t, he won’t. Or at least he shouldn’t. That’s what many political scientists believe: When it comes to nomination battles, the party decides.

The Republicans have already gone through this process with a party elder in the 2016 cycle. Remember the Mitt Romney boomlet? Back in January, the 2012 standard-bearer semi-publicly thought about running again. But Jeb Bush moved forcefully to lock up old Romney donors and make it clear he intended to run as the choice of the establishment.

Mr. Romney backed down. Or to put it another way, he lost.

“Just to be clear: Romney didn’t consider whether to run and then decided against it. He ran for president for 2016. He tried. Failed. Dropped out,” wrote political scientist Jonathan Bernstein in his Bloomberg View column at the time.

Of course, in some ways Biden has already lost, too. Hillary Clinton wrapped up the vast majority of Democratic Party insiders long ago. Her endorsement list is a party “who’s who.”

Back in May, David Byler of RealClearPolitics ran the numbers and declared that Mrs. Clinton “seems to be dominating the Democratic invisible primary.”

She still is. Yes, her numbers are slipping. Some party leaders are getting nervous. But she’s still 25 percentage points ahead of Bernie Sanders – and 35 points ahead of Biden – in the RealClearPolitics rolling average of major polls.

But in the invisible primary, results can reverse. They’re unlike actual primaries in that way. Clinton’s problems have given Biden new hope and caused him to revive his presidential ambitions.

So he’s out on the road, getting treated like a candidate. On Wednesday morning, the VP took a helicopter out to Andrews Air Force Base to board Air Force Two for a flight to Florida. He saluted on the tarmac, chatted with the flight commander, and boarded the plane with a wave to the cameras.